In a typical multi-engine aircraft electrical system for which the invention is particularly suited, each engine drives a generator through a constant speed drive. Each of the engine driven generators powers a set of load circuits and the load circuits may be interconnected through an electrical distribution bus. An auxiliary power unit drives an auxiliary generator to supplement the engine driven generators in the event of an engine or generator failure. The auxiliary power unit is also used to provide electric power with the aircraft on the ground when the engine are shut down and an external power source is not readily available.
A generator control unit (GCU) for each of the generators monitors the electrical condition of the associated generator and conditions of the mechanical drive to the generator. A bus power control unit (BPCU) monitors power distribution throughout the system and the condition of the generators, and controls bus tie breakers which connect the electrical distribution bus between the generators, loads and the auxiliary generator. One or both loads are powered by one of the available generators. Two generators are not, however, connected in parallel. The control units have in the past coordinated interlock information using multiple hard wired circuits.
In accordance with the invention, the generator control units and the bus power control unit utilize integrated circuit microprocessors which have several advantages including functional flexibility and improved reliability.
Interconnection is provided between the bus power control unit and each of the generator control units through serial data links. Input and output information may be shared by the BPCU and each of the GCU's, minimizing the interconnecting wiring required between the control units, the generators and the sensors and circuit breakers for the electrical distribution system.
Redundant informaion concerning generator and distribution circuit conditions may readily be collected and compared without the addition of hardware and wiring.
The microprocessor control units enable the utilization of multiple time delays in the control program. The time delays are based on the microprocessor clock frequency and have an inherent accuracy much higher than that of a discrete component timer. Accordingly, time limits for the operation of related circuits may be shortened as it is not necessary to accommodate the large time tolerances of discrete component timers. Moreover, additional weight and component space is not required for each timer and more and different time delays may be utilized where desirable.
Many of the control functions are based on software programing of the microprocessors. Changes may readily be made to accommodate different system requirements.
Another feature of the invention is the provision of a method of controlling the system in which each of the GCU's is operated in accordance with conditions of the associated generator and the BPCU is operated in accordance with electrical distribution circuit conditions and together they control the circuit and tie breakers.
Yet a further feature is the provision of a voltage regulator in which an average of the generator phase voltages is corrected by an error signal to control the generator field current source and having means for sensing an abnormally high phase voltage to disable the summing means and operate the field current source from the error signal.